The term "asphalt cement," as used in the description of the present application refers to any of a variety of solid or semi-solid materials at room temperature which gradually liquify when heated and in which the predominant constituents are bitumens which are obtained as residue in petroleum refining. Asphalt is further defined by Kirk Othmer, Encyclopedia of Chemical Technology, Vol. 3, 3rd Ed. (1978), pages 284-327, John Wiley & Sons, New York. An additional discussion appears in the publication entitled "A Brief Introduction to Asphalt and Some of Its Uses," Manual Series No. 5 (MS-5), The Asphalt Institute 7th Edition, September 1974. Both of these references are hereby incorporated by reference.
Asphalt containing rubber has been evaluated in the past. Rubberized asphalt is too viscous for easy mixing and handling. Oil can be added to reduce the viscosity, but this yields an asphalt cement that tends to flow more than an asphalt cement without oil. This flow could result in "rutting" if such an asphalt cement were applied to a highway.
Asphalt cements have found particular utility when combined with aggregates. Such combinations generally are referred to as "asphalt concrete" and are employed extensively as paving compositions for roads, roofs, driveways, parking lots, airport runways, etc. The asphalt cement is converted to a fluid state when paving a road. One fluid form is a suspension or emulsion of the asphalt cement in water. After spreading or compressing the aggregate containing asphalts, water evaporates or separates and the asphalt hardens into a continuous mass. Another form of asphalt employed in road construction is a cutback, i.e. a liquid petroleum product produced by fluxing an asphaltic base with a suitable organic solvent or distillate. A road is formed by paving the aggregate containing cutback and evaporating the volatile distillate from the mass. An advantage of using the above road construction techniques is the avoidance of high temperature application. In an alternative and most widely used technique, the asphalt cement and aggregate can be mixed and applied at elevated temperatures at the fluid state of the asphalt cement to form the road.
U.S. Pat. No. 3,010,926 (Odasz, et al, Nov. 28, 1961), relates to asphaltic compositions and more particularly to compositions consisting essentially of asphalt having minor proportions of rubber interblended therewith or intimately dispersed therein, herein designated "rubberized asphalt." The reference provides such asphaltic compositions having novel and highly useful physical and chemical properties and also provides a commercially practical and economical method for producing such compositions and for regulating and controlling the properties thereof.
U.S. Pat. No. 4,621,108 (Burris, Nov. 4, 1986), relates to a base stock composition comprising a blend of gilsonite asphalt and a rubber latex residue. The base stock may be used alone as a paving material or emulsified to form a gilsonite emulsion having a variety of uses.